Arrangement and process for treating a surface

ABSTRACT

An apparatus and method for treating a surface with a jet utilizing a multiplicity of particles, using a mixing chamber for mixing a stream of propellant gas with the multiplicity of particles, a particle generator, which is designed to generate the multiplicity of particles and introduce them into the mixing chamber in a solid state, the particle generator having at least one screen plate, and it being possible for the multiplicity of particles to be formed in a solid state by pressing a solid starting material through the screen plate, a propellant gas line with a propellant gas nozzle for introducing the propellant gas into the mixing chamber, and an outlet from the mixing chamber for the stream of propellant gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 of International PCT Application No. PCT/EP2017/081737, filed Dec. 6, 2017, which claims priority to German Patent Application No. DE 10 2016 123 812.0, filed Dec. 8, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND

The invention relates to an arrangement and a process for treating a surface, in particular with a jet comprising a multiplicity of particles.

In many situations, a surface has to undergo mechanical cleaning. It may for instance be necessary in the production of wires for example to clean the finished product to ensure product quality. In solutions known for doing this, a wide variety of chemical and/or mechanical cleaning processes are used. The following come into consideration for example: grinding, brushing, ultrasonic exposure or superheated steam treatment. In particular, it is also known to treat surfaces with a jet of carbon dioxide particles.

These processes are also used in the production of plastic products for removing flash from a surface of the plastic products produced.

A combination of a number of the processes mentioned is often used to achieve the result that is respectively desired in the case of the applications described. However, the results are nevertheless often inadequate and not reproducible and the processes too laborious, with the result that they represent a limiting factor for product quality and also production speed.

In known processes in which carbon dioxide particles are used it is in particular the case that the particle size is not constant and not controllable, with the result that a uniform stream of particles cannot be achieved. In particular, there may be a pulsation of the stream of particles. Uniform cleaning or removal of flash or burr, in particular with a reproducible result, is not readily possible. Often, the process has to be repeated a number of times, at least for individual regions of a surface to be treated. Situations in which the kinetic energy of the carbon dioxide particles is not sufficient are also known. In that case, a larger particle size would be desirable. Although it is attempted to achieve this in the prior art, known solutions with particularly large particles have the disadvantage that the particle size can vary greatly. Furthermore, known solutions with particularly large particles are often susceptible to faults, in particular in the case of an automated configuration.

SUMMARY

On this basis, the object of the present invention is to overcome at least partially the technical problems described in connection with the prior art. In particular, an arrangement for the treatment of a surface with which particularly uniform and particularly intensive treatment of the surface is possible is intended to be presented. A corresponding process is also intended to be presented.

These objects are achieved by an arrangement and a process for treating a surface according to the features of the independent patent claims. Further advantageous refinements of the arrangement and of the process are provided in the respectively dependently formulated patent claims. The features set out individually in the patent claims can be combined with one another in any desired, technologically meaningful way and can be supplemented by explanatory substantive matter from the description, demonstrating further variants for the configuration of the invention.

According to the invention, an arrangement for treating a surface with a jet comprising a multiplicity of particles is presented. The arrangement comprises at least:

-   -   a mixing chamber for mixing a stream of propellant gas with the         multiplicity of particles,     -   a particle generator, which is designed to generate the         multiplicity of particles and introduce them into the mixing         chamber in a solid state, the particle generator having at least         one screen plate, and it being possible for the multiplicity of         particles to be formed in a solid state by pressing a solid         starting material through the screen plate,     -   a propellant gas line with a propellant gas nozzle for         introducing the propellant gas into the mixing chamber, and     -   an outlet from the mixing chamber for the stream of propellant         gas.

The arrangement described is used for example in particular in the production of wire and plastic products, but can also be used in other applications, in particular in principle in the case of carbon dioxide jets. With the arrangement described, for example, cleaning of the surface of a produced wire or of a produced plastic product can be carried out. Flash or burr may also be removed from the surface of a produced wire or plastic product. Removing flash or burr means that excess material is removed from the surface. The excess material may be formed in particular as flash or burr at those places at which parts of a casting mould have been put together and/or at which an inlet for casting material into the casting mould is provided.

The solid starting material from which the particles are formed is preferably a substance that is liquid or gaseous at room temperature. In particular when the substance is gaseous at room temperature, the treatment of a surface can be carried out without residues of the substance remaining on the surface. The substance is preferably carbon dioxide.

In order to generate the jet comprising the multiplicity of particles, first the stream of propellant gas is provided. This may be performed for example by a compressor. The stream of propellant gas is preferably a stream of compressed air. However, a gas other than air, such as for example nitrogen or carbon dioxide, may also be used.

The mixing chamber is a space that is closed off with the exception of the openings described. Said openings are in particular an opening of the propellant gas nozzle, and the outlet. The propellant gas nozzle is preferably situated on a side of the mixing chamber that is opposite the outlet.

The suitability of the mixing chamber for mixing the stream of propellant gas with the particles should be understood as meaning that the mixing chamber is configured and connected to the particle generator in such a way that, after passing through the mixing chamber, the stream of propellant gas comprises the multiplicity of particles.

The particle generator is preferably configured in such a way that the solid starting material can be pressed against the screen plate by way of a conveying screw or by way of a pneumatic or mechanical press. For this purpose, the particle generator preferably has a particle generator chamber with an inlet through which the starting material can be introduced. This can take place already in the solid state or alternatively also in the liquid state. In the latter case, the particle generator chamber is preferably subjected to temperature control or cooled in such a way that the starting material is transformed into the solid state on the path from the inlet to the screen plate. The solid starting material can preferably be transported through the particle generator chamber by means of the conveying screw or by means of the pneumatic or mechanical press. The solid starting material preferably takes a form which allows such transport through the particle generator chamber. This means in particular that the solid starting material does not have to be a solid block. The solid starting material may also be subdivided into a multiplicity of small parts. The solid starting material may also for example take the form of pressed snow.

The particle generator chamber is preferably configured in a concentric manner around the propellant gas line. Furthermore, the screen plate is preferably of circular configuration, in particular with a cutout for the propellant gas line or for the propellant gas nozzle. The cutout is preferably arranged in the centre of the screen plate. The cutout is preferably of circular configuration. A round propellant gas line or propellant gas nozzle in the centre of a round screen plate makes it possible to achieve particularly uniform mixing of the stream of propellant gas with the particles. In particular, a round jet can be generated. Such a jet is preferred for most applications.

The screen plate preferably has a multiplicity of openings. The openings in the screen plate are preferably of circular configuration. The openings allow the solid starting material to be pressed through the screen plate, with the result that the particles can be formed. The particles have a particle diameter which results from an opening diameter of the openings. Consequently, the particle size can be controlled by selecting the opening diameter of the openings. The opening diameters of the openings in the screen plate preferably lie in the range from 0.5 mm to 5 mm [millimetres], in particular in the range from 1 mm to 3 mm. By way of the particle size, it is possible in particular to influence the particle mass and thus also the impact energy with which the particles strike the surface. The higher the impact energy, the greater the abrasiveness that can be achieved. For example, in the case of light soiling and/or in the case of sensitive surfaces, such as for example in the case of a plastic surface, an opening diameter of 0.5 mm to 2 mm [millimetres] is preferably selected. In the case of heavier soiling and/or in the case of more insensitive surfaces, such as for example in the case of metal surfaces, an opening diameter of 1 mm to 5 mm [millimetres] is preferably selected.

Preferably, the arrangement is configured in such a way that the screen plate is easily replaceable. In that case, it is possible for the particle size to be adapted to the requirements of different applications by selecting from different screen plates. In some applications, a uniform particle size may be desired. In other applications, it may be appropriate for example to simultaneously blast particles with different sizes onto the surface to be treated. Correspondingly, the opening diameters of all openings may be equal in size or different.

The generation of particles by means of the particle generator allows particularly large particles to be provided and mixed with the stream of propellant gas. The particles can thus in particular be larger than those that can be formed for example by atomization of liquid carbon dioxide. Larger particles can have greater kinetic energy, and can therefore have a greater effect in the treatment of the surface. For example, with large particles, heavy soiling of a surface can be removed. The fact that the screen plate makes it possible to generate large particles of a uniform size means that a great and also uniform effect can be achieved with the arrangement described, and so in particular a reproducible cleaning performance can be achieved.

The arrangement, and in particular the component parts of the arrangement that can come into contact with the substance, in particular with the solid starting material, and/or with the particles, is/are preferably formed with a material that can withstand the low temperatures to be expected when that happens. In the case of solid carbon dioxide, the temperature may for example be approximately −80° C. Steel in particular, preferably high-grade steel, is preferred as the material for the arrangement.

The stream of propellant gas can be introduced into the mixing chamber through the propellant gas line, and the particles can be introduced into the mixing chamber through the screen plate. Preferably, the particles are introduced into the mixing chamber in the direction of the stream of propellant gas. This results in the entire mixing chamber being available for mixing the stream of propellant gas with the particles. The stream of propellant gas mixed with the particles can exit the arrangement through the outlet from the mixing chamber for the stream of propellant gas. The outlet is preferably configured with a circular cross section. This can make a round jet possible. In order to achieve mixing of the stream of propellant gas with the particles that is as uniform as possible, the propellant gas nozzle, the mixing chamber and the outlet are configured and arranged in such a way that it is possible to generate a flow in which the particles can be mixed with the stream of propellant gas by swirling.

In a preferred embodiment of the arrangement, the propellant gas nozzle is configured as a Laval nozzle.

A Laval nozzle is especially suited for mixing the stream of propellant gas uniformly with the particles.

In a further preferred embodiment of the arrangement, at least the mixing chamber and the propellant gas nozzle are configured to be rotationally symmetric about an axis of the arrangement.

In this embodiment, it is in particular possible to generate a round jet. This is advantageous for many applications, as described further above.

In a further preferred embodiment of the arrangement, the particle generator furthermore has a conveying screw, which is designed to press the solid starting material through the screen plate.

The conveying screw is preferably configured in such a way that the solid starting material can be transported from the inlet into the particle generator chamber to the screen plate. Furthermore, the solid starting material can be pressed through the screen plate by means of the conveying screw. The conveying screw can thus serve two functions. In particular, the conveying screw can allow particles to be generated continuously. Consequently, the arrangement is able to continuously generate a jet for treating the surface.

In a further preferred embodiment of the arrangement, the mixing chamber is configured at least as part of an outer Laval nozzle.

As described further above, the propellant gas nozzle, the mixing chamber and the outlet are configured and arranged in such a way that it is possible to generate a flow in which the particles can be mixed with the stream of propellant gas by swirling. Such a flow can be generated in particular in the manner of a Laval nozzle.

In a further preferred embodiment of the arrangement, the particles are formable at least partially with solid carbon dioxide.

Carbon dioxide has the advantage that, immediately after striking the surface to be treated, it is transformed into the gaseous state without leaving any residue. According to a further aspect of the invention, a process for treating a surface with a jet comprising a multiplicity of particles is presented, an arrangement as described being used.

The particular advantages and design features of the arrangement that are described further above are applicable and transferable to the process described, and vice versa.

In a preferred embodiment of the process, the multiplicity of particles is generated by a solid starting material being pressed through a screen plate.

In a further preferred embodiment of the process, the solid starting material comprises carbon dioxide, in particular carbon dioxide snow.

In a further preferred embodiment of the process, the treating of the surface comprises at least one of the following steps:

-   -   cleaning the surface, and     -   removing flash or burr from the surface.

The specified steps may be carried out alternatively or cumulatively, that is to say that a surface may just be cleaned, just have flash or burr removed or both be cleaned and have flash or burr removed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the technical environment are explained in more detail below on the basis of the FIGURE. The FIGURE shows a particularly preferred exemplary embodiment, to which, however, the invention is not restricted. In particular, it should be pointed out that the FIGURE, and in particular the relative sizes represented, is/are only schematic. In the FIGURE:

FIG. 1 schematically shows a lateral sectional representation of an arrangement for treating a surface.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a lateral sectional representation of an arrangement 1 for treating a surface with a jet comprising a multiplicity of particles. The arrangement 1 comprises a mixing chamber 2 for mixing a stream of propellant gas with the multiplicity of particles. The arrangement 1 furthermore comprises a particle generator 8, which is designed to generate the multiplicity of particles and introduce them into the mixing chamber 2 in a solid state. The particle generator 8 has a screen plate 10 and a conveying screw 9. The multiplicity of particles can be formed in a solid state by pressing a solid starting material 12 through the screen plate 10 by means of the conveying screw 9. The particle generator 8 preferably has a particle generator chamber 14 with an inlet 13 through which the starting material or a substance for producing the starting material can be introduced. In this case, liquid carbon dioxide for example can be expanded through the inlet 13 into the particle generator chamber 14, with the result that solid carbon dioxide is formed as solid starting material and carbon dioxide gas in the particle generator chamber 14.

The arrangement 1 furthermore has a propellant gas line 3 with a propellant gas nozzle 4 configured as a Laval nozzle 5, which serves for introducing the propellant gas into the mixing chamber 2. The arrangement 1 also has an outlet 7 from the mixing chamber 2 for the stream of propellant gas. The mixing chamber 2 is configured as part of an outer Laval nozzle 11.

The mixing chamber 2 and the propellant gas nozzle 4 are configured to be rotationally symmetric about an axis 6 of the arrangement 1. Also, the outlet 7 is of round configuration.

With the arrangement presented and the process presented for treating a surface, a particularly uniform and particularly intensive treatment of the surface can be achieved. In this case, it is possible to use particularly large carbon dioxide particles having high kinetic energy, which have a particularly uniform and particularly well controllable particle size. This applies in particular to cleaning and removing flash or burr. The arrangement and the process may be used in particular in the production of wire or plastic products.

LIST OF DESIGNATIONS

-   1 arrangement -   2 mixing chamber -   3 propellant gas line -   4 propellant gas nozzle -   5 Laval nozzle -   6 axis -   7 outlet -   8 particle generator -   9 conveying screw -   10 screen plate -   11 outer Laval nozzle -   12 solid starting material -   13 inlet -   14 particle generator chamber

It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above. 

1.-10. (canceled)
 11. An apparatus for treating a surface with a jet comprising a multiplicity of particles, the apparatus comprising: a mixing chamber for mixing a stream of propellant gas with the multiplicity of particles, a particle generator, configured to generate the multiplicity of particles and introduce them into the mixing chamber in a solid state, the particle generator comprising at least one screen plate, wherein the multiplicity of particles are formed in a solid state by pressing a solid starting material through the at least one screen plate, a propellant gas line with a propellant gas nozzle configured to introduce the propellant gas into the mixing chamber, and an outlet from the mixing chamber for the stream of propellant gas.
 12. The apparatus of claim 11, wherein the propellant gas nozzle is configured as a Laval nozzle.
 13. The apparatus of claim 11, wherein the at least the mixing chamber and the propellant gas nozzle are configured to be rotationally symmetric about an axis of the apparatus.
 14. The apparatus of claim 11, wherein the particle generator further comprises a conveying screw), configured to press the solid starting material through the at least one screen plate.
 15. The apparatus of claim 11, wherein the mixing chamber is configured at least as part of an outer Laval nozzle.
 16. The apparatus of claim 11, wherein the particles is formable at least partially with solid carbon dioxide.
 17. A process for treating a surface with a jet comprising a multiplicity of particles, utilizing an apparatus according to claim
 11. 18. The process according to claim 17, wherein the multiplicity of particles are generated by a solid starting material being pressed through the at least one screen plate.
 19. The process according to claim 18, wherein the solid starting material comprises carbon dioxide.
 20. The process according claim 17, wherein the treating of the surface comprises at least one of the following steps: cleaning the surface, and removing flash or burr from the surface. 